1/4 Wavelength Ground Plane

The 1/4 wavelength ground plane antenna is very simple in its construction and is useful for communications when size, cost and ease of construction are important. This antenna is designed to transmit a vertically polarized signal. It consists of a 1/4 wave element as half-dipole and three or four 1/4 wavelength ground elements bent 30 to 45 degrees down. This set of elements, called radials, is known as a ground plane. This is a simple and effective antenna that can capture a signal equally from all directions. To increase the gain, the signal can be flattened out to take away focus from directly above and below, and providing more focus on the horizon. The vertical beamwidth represents the degree of flatness in the focus. This is useful in a Point-to-Multipoint situation, if all the other antennas are also at the same height. The gain of this antenna is in the order of 2 to 4 dBi.

Figure 4.8: Quarter wavelength ground plane antenna.